Polyethylene terephthalate (PET) is formed into containers using a two-step process. First, a tube-shaped preform is injection molded. Second, the preform is heated above its glass transition temperature and blown into a mold with high pressure air in order to shape it into a bottle.
A quartz infrared lamp is used to “reheat” the preform in the second stage. Typical lamp temperatures are 2500–3000° K, having a broad emission spectrum in the range of 500 to 2000 nm. The emission maximum is around 900 to 1000 nm. PET absorbs energy poorly in the region of 500–2000 nm. Thus, in order to maximize energy absorption from the lamps and increase the preform's “reheat” rate, infrared absorbing compounds are sometimes added to PET. Unfortunately, these materials also cause a negative effect on the visual appearance of the PET bottle, causing it to darken (lower L*). Thus, there remains a need to improve the reheat rate of PET preforms while minimizing the impact such an additive would have on L*.